The present invention relates to a control valve, and, more particularly, it is concerned with an electromagnetic control valve which proportionately controls the flow-rate of a fluid by electrical means.
Heretofore, this type of electromagnetic proportional control valve was of such a construction as shown in FIG. 3 of the accompanying drawing. In more detail, in FIG. 3, the electromagnetic proportional control valve generally designated by a reference numeral 1 is mainly constructed with an electromagnetic control section 2 and a flow-rate control section 3. The electromagnetic control section 2 is to control the flow-rate of a fluid at the flow-rate control section 3 to be described later, and is constructed with a plunger 4 as a movable part which is in contact with a spool 17 disposed at one end of the plunger in its axial direction (the bottom end side in the drawing); a cylinder 5 which slidably supports the plunger; a core 6 which secures the upper end of the cylinder 5 and one end of which is in the interior of the cylinder to oppose the above-mentioned plunger 4; a winding 8 wound on and around a bobbin 7 which is disposed on the circumference of the cylinder 5 so that it may cooperate with the core 6 to attract the plunger 4; a spring 9 which is interposed between the plunger 4 and the core 6 to energize the plunger 4 in the direction opposite to the electromagnetic force owing to the winding 8 and the core 6 (the downward direction in the drawing); and a spring 18 which energizes the plunger 4 in the direction of the electromagnetic force (the upward direction in the drawing) by way of the spool 17.
Each of these component parts is housed and disposed in a space formed by a casing 10 in the shape of an inverted tumbler glass or the like with its open end facing downward and a spacer 11 to close the open end of the casing. By the way, the spacer 11 has at the substantially center part thereof an opening 11a, through which the lower end of the cylinder 5 is to pass. Further, in FIG. 3, a reference numeral 12 designates a threaded screw for fixedly securing the upper end part of the core 6 to the side of the casing 10.
On the other hand, the flow-rate control section 3 has a body 13 joined to the outside of the spacer 11 and to the side of the above-mentioned electromagnetic control section 2 in its axial direction. Further, in the axial direction of the body 13, there are formed in series a holding bore 13a of a large diameter for housing and perforating the bottom end part of the cylinder 5 with the plunger 4 being accommodated therein; a small bore 13b, into which is positioned a sleeve 14, and which is formed in continuity with the large bore 13a and slidably supporting the spool 17; and a communicating bore 13c which is continuous with the small bore and open to the lower end of the body 13. In addition, at the bottom end and the lateral part of this body 13, there are fixedly provided tube bodies 15 and 16, one of which (the tube body 15) is connected to the communicating port 13c of the body 13, and the other of which (the tube body 16) is connected to the small bore 13b, where the above-mentioned sleeve 14 is to be fitted, with its end being open to a part of the peripheral wall part thereof. In the outer peripheral wall part of the sleeve 14 fitted into the small bore 13, there is formed a slit 14a in the axial direction so as to be communicatively connected with the fluid passage-way formed by the tube body 16. The opening area of this slit 14a is determined by its being opened and closed by the spool 17 which slides within the sleeve 14, as the consequence of which the flow-rate of the fluid flowing in this part is controlled.
The above-described electromagnetic control section 2 and flow-rate control section 3 are positioned in their axial direction by the lower outer peripheral part of the cylinder 5, in which the plunger 4 is housed, and the inner peripheral part of the holding bore 13a of the body 13, and are fixedly assembled.
In the following, explanations will be given as to the function of this conventional electromagnetic proportional control valve. When electric current is caused to pass through the winding 8, the electromagnetic force (force of attraction) commensurate with the input current acts on the plunger 4 by way of a magnetic circuit constructed by the casing 10, the core 6, the spacer 11 and the plunger 4, and the plunger 4 moves to a position where this electromagnetic force and an energizing force of the spring 9 and the spring 18 interposed between the plunger 4 and the core 6, together with the movement of which the spool 17 which slides within the sleeve 4 control the slit 14a to open and close, whereby the flow-rate of the fluid is controlled to a desired quantity.
In FIG. 3, the fluid which has been forwarded under pressure from the arrowed direction (leftward direction in the drawing) passes through the slit 14a, after which it is reduced its pressure, and flows in the arrowed direction (downward direction in the drawing). At that time, both discharge chamber 20 and air-gap chamber 19 are communicatively connected by pressure levelling ports 4a and 17a.
The conventional electromagnetic control valve 1 as described in the foregoing has its own disadvantage such that, even when the spool 17 reaches its condition for perfectly closing the slit 14a at the time of non-conduction of the electric current through the winding, there unavoidably exists between the sleeve 14 and the spool 17 a gap for permitting the spool 17 to slide within the sleeve 14 in the up-and-down direction, on account of which the fluid to be controlled leaks out, thereby making it impossible to perfectly prevent the fluid to be controlled from leaking through this gap. Moreover, in order to prevent the fluid from leaking, it was contemplated to provide an electromagnetic valve for closure in front of the tube body 16 in the fluid influent section, in which case, however, there arose such a problem that number of the component parts increased, and, at the same time, its manufacturing cost became high.